1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
2. Description of the Related Art
High temperature gate bias (HTGB) tests are conducted with respect to metal oxide semiconductor field-effect transistors (MOSFET) that use silicon carbide (SiC). In a HTGB test, voltage is applied between a gate and a source for a long period of time in a high temperature environment. During the HTGB test, a threshold voltage (Vth) between the gate and source is known to decrease.
The threshold voltage decreases consequent to the diffusion of an impurity from an external source. A method of forming, for example, a titanium (Ti) alloy that prevents the diffusion of impurities into the surface of the MOSFET has been disclosed to suppress decreases in the threshold voltage (for example, refer to Japanese Laid-Open Patent Publication No. 2012-129503). The diffusion coefficient of a silicon nitride film is smaller than that of a silicon oxide (SiO2) film, thus use of a silicon nitride (SiN) film is also conceivable to prevent the diffusion of impurities (for example, refer to Perkins, W. G., et al, “Diffusion and Permeation of He, Ne, Ar, Kr, and D2 through Silicon Oxide Thin Films”, J. Chem. Phys., Vol. 54, No. 4, pp. 1683-1694, (1971); and Arnoldbik, W. M., et al, “Dynamic behavior of hydrogen in silicon nitride and oxynitride films made by low-pressure chemical vapor deposition”, Phys. Rev. B, Vol. 48, No. 8, pp. 5444-5456, (1993)).